:A more realistic worst-case: Say somebody reads mouse direction (COM=LOW), and immediately thereafter the scroll wheel (COM2=LOW). In that case you may have only 10-20 clock cycles, so COM would need to raise relative fast, else the 74LS240 would be still selected when reading the wheel. With pull-up it'd be be plenty of time, but if it gets pulled up "through the air" it could be a problem.
:Anyways, I haven't tried, so maybe there's no problem at all. Until some days ago I didn't even knew that COM and COM2 are open collector outputs, so I guessed many people could be trapped there, expecting stable HIGH levels on that pins. Ciao, --[[User:Nocash|Nocash]] 19:11, 18 April 2010 (UTC)
Hi Nocash, Yes, that exact situation you describe, could cause a misread and in that case the AY could read a 1 instead of a 0 (or vice versa), but only at the start or end of every movement, that means, if you move the mouse across the screen, say, 200pixels, then worst case, it had 2 misreads (misreads "mid-movement" aren't possible because the bit didn't change). Even if it did misread (on the very first or last pulse), then the cursor moved 199 pixels, instead of 200 pixels, is that really a big deal? Is anyone even going to notice? I very much doubt it, and removing this tiny flaw would cost additional hardware, so it's really not worth the bother. And as I've said before, my goal is to create easy projects, that anyone can build and most importantly - don't cost very much.